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Old 02-09-2021, 07:01 PM   #1
toyebox
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Default Piston to valve contact help

Good day, and thank you in advance for any and all assistance.

Background:

Built 2015 short block with Manley rods and pistons (not built by me). Block was disassembled, crank and rods broken down, everything inspected. Only thing that seemed odd was #4 rod seems a tad tight on the crank compared to the rest, but spun smooth none the less. Block was fully assembled, torque specs and patterns followed to the letter from the FSM. the only thing I failed to do was check wrist pin clearances. Block has never been decked as far as I know, and surfaces were straight.

Heads came from another 2015 block that had low compression. Checked to make sure valves didn't leak by first, then removed the cams and buckets to inspect. Did not remove springs or valves. There is little info known about the motor that the heads came off of, except that it went low compression, and after inspection it wad rings. The driver side head buckets were mixed up when I received it (the person who gave them to me accidentally did it), so I bench checked everything to get the buckets back in the right locations. I failed here as well, as I forgot they needed to be torqued to the block for a perfectly accurate measurement. When installing the head though, the buckets were in the right spots by my account.

Fully assembled the long block, new OEM gasket kit, and ARP head studs. Again, all torqued correctly. Rods, bearings. Pistons, etc were all for sure installed in the correct orientation. Unfortunately I did not take valve lash measurements after installing heads.

Onto the issue. On first start, there was a noticable tap, which seemed to be clearly coming from #4 valvetrain area. It most definitely does not sound like rod knock.

I've pulled the motor and driver side head. Attached are two pictures from what looks like to me like piston/valve contact. The problem though is, it doesn't seem like the marks on the piston could have come from the valves, given where the marks are. I could be completely wrong here though. I've also listed the valve lash prior to removing the head.

#2 exhaust fwd 0.30 good / 0.33 no good
#2 exhaust - rear 0.30 good / 0.33 no good
#4 exhaust - fwd 0.30 good / 0.33 no good
#4 exhaust - rear 0.33 good / 0.35 no good
#2 intake - fwd 0.20 good / 0.23 no good
#2 intake - rear 0.20 good / 0.23 no good
#4 intake - fwd 0.20 good / 0.23 no good
#4 intake - rear 0.20 good / 0.23 no good

It seems the exhaust side is tight all around with 0.35mm being the target.

So my question is, is what's next? What should be checked. By my assumption:

-valves should be checked to make sure they weren't bent
-wrist pin clearance should be checked
-rod to crank clearance

What else could cause this? Again, I'm under the assumption that neither the heads or block were ever decked, given the information I received.

I would like to do all work in house, without using a shop. I'm on an island, were the shops are... Not ideal and very expensive.

Thank you very much!
Matthew

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Old 02-10-2021, 11:10 AM   #2
cboggess
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That pic of the piston is not from the valves. The contact point would show in the valve relief on the piston.
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Old 02-10-2021, 11:40 AM   #3
toyebox
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Quote:
Originally Posted by cboggess View Post
That pic of the piston is not from the valves. The contact point would show in the valve relief on the piston.
That's why I said that I didn't think the marks on the piston were made by the valves. There does still seem to be both contact with the valves and possibly head though, based on both pictures.
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Old 02-10-2021, 02:21 PM   #4
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Quote:
Originally Posted by toyebox View Post
That's why I said that I didn't think the marks on the piston were made by the valves. There does still seem to be both contact with the valves and possibly head though, based on both pictures.
Most of the time when I see this issue it's due to time being off. You get 3 teeth of room on the cam gear before they touch.

I will agree that yours have hit something, but as to the reason why I think it's still a mystery.
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Old 02-10-2021, 03:30 PM   #5
Jedi03
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what crank are you using and what length are the rods?
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Old 02-10-2021, 05:22 PM   #6
toyebox
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Quote:
Originally Posted by Jedi03 View Post
what crank are you using and what length are the rods?
Stock 2015 sti crank. Unfortunately there are zero part numbers on the rods. I was told they are Manley rods. Any sort of measurements I can take with the short block assembled?

Quote:
Originally Posted by cboggess View Post
Most of the time when I see this issue it's due to time being off. You get 3 teeth of room on the cam gear before they touch.

I will agree that yours have hit something, but as to the reason why I think it's still a mystery.
Timing was 100% dead on. Cam sprockets would only go on one way, given there was only one dowel hole per sprocket that would fit.

Can play in the wrist pin cause this?
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Old 02-10-2021, 07:46 PM   #7
cboggess
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Quote:
Originally Posted by toyebox View Post
Stock 2015 sti crank. Unfortunately there are zero part numbers on the rods. I was told they are Manley rods. Any sort of measurements I can take with the short block assembled?



Timing was 100% dead on. Cam sprockets would only go on one way, given there was only one dowel hole per sprocket that would fit.

Can play in the wrist pin cause this?
That would have to be a CRAZY amount of play in the wrist pin, and you'd have signs of it smacking the head (Impression of the quench ring on the piston) for that to be the problem.

Measure piston protrusion with it at top dead center.
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Old 02-10-2021, 08:07 PM   #8
toyebox
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Quote:
Originally Posted by cboggess View Post
That would have to be a CRAZY amount of play in the wrist pin, and you'd have signs of it smacking the head (Impression of the quench ring on the piston) for that to be the problem.

Measure piston protrusion with it at top dead center.
Good to know. I'll take the measurement tomorrow morning. I'm starting to think there is definitely something up with the rod for #4 (the problem cylinder). Pulled pistons for #2 and #4 and #4 is tight on the crank, and not smoothly rotating. It loosens up and then gets tight again. There is no up and down play at all, and very minimal side to side play. Before I broke down the short block the first time it felt similar. Could this be causing the issue.
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Old 02-11-2021, 08:44 AM   #9
Elbert Bass
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Valve contact would be evident in the moon shaped recesses. That piston contact is from something bouncing around in the cylinder, possibly trash from the intake or not being diligent in keeping things clean during assembly.

I have seen that before - watched a guy replace a new short block and both heads twice - he forgot to clean out the manifold after an engine leaned out and demolished pistons with detonation. Folks don't realize once a piston comes apart it's like a big vacuum leak when the intake valves open - anything loose gets sucked up into the intake.

That valve mark does appear to look like piston contact, but the piston does not show it - at least in the picture you show of part of the piston face. Possibly what ever dinged the piston. Do you have a wider shot of that piston face?
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Old 02-11-2021, 09:29 AM   #10
BlackFighter
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It looks like the pistons were dropped or banged with a hammer during assembly, and the head valves were turned over during disassembly and were contacted together by hand without realizing it when removing the heads during this disassembly.

It looks like a fresh contact. If it happened a long time ago then you would not be able to see those marks on the valve, would have been covered over. If it was a constant on going contact, then you would see marks in the valve indents in the piston.
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Old 02-11-2021, 11:02 AM   #11
Jedi03
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the description above sounds like what happened to me...I dropped a piece of a runner (doing tgv deletes on the car, bad idea) into the cylinder and it would bind up due to that piece taking up the little bit of space the pistons had...do you have the heads off now? you can check some of the protrusion with rotating the crank and see what the piston does...if it is apart too its easy to remove the pistons to check for bearing issues and play as well
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Old 02-11-2021, 09:51 PM   #12
toyebox
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Thanks for the input so far. New information..

Removed the other head and it seems #3 piston also had clearance issues. #1 and #2 looked perfect.

I would find it extremely hard to believe if it was metal particulate that caused the damage to the piston tops. Everything was cleaned meticulously prior to installing--all new oil pump, water pump, turbo used. Intake manifold was flushed and cleaned three times, including running a fine brissle brush through it. Top mount was also cleaned extremely well.

Are there any other ideas of why only #3 and #4 would have these issues. Thank you.
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Old 02-11-2021, 11:16 PM   #13
BlackFighter
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How do you know if it was not built by you. Like you stated
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Old 02-12-2021, 01:06 AM   #14
toyebox
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Quote:
Originally Posted by BlackFighter View Post
How do you know if it was not built by you. Like you stated
I also stated that I broke the short block down and inspected everything prior to reassembling.
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